Knee airbags are being increasingly used in the automobile industry. They serve essentially for two purposes, namely, to protect the knee-tibia region against impact with a generally hard instrument panel, on the one hand, as well as to prevent the forward displacement of the pelvis of the passenger to be protected in case of an accident, in particular when the latter is not buckled in.
It is advantageous in many applications to connect the knee airbag to the vehicle by means of its posterior end, so that the connection point is located at a lower point of the instrument panel or even in a transition area between the instrument panel and the foot well cover panel (so-called “low mount concept”). If the knee airbag is mounted in this way, provisions must be made to ensure that the expanding airbag follows essentially the convex shape of the instrument panel, so that it has a kind of “banana shaped” cross section. Several proposals have already been made by which this can be accomplished.
DE 10 2007 005 304 A1, for example, describes a knee airbag in which the side wall of the airbag envelope that faces toward the instrument panel, which also constitutes the support surface, is shortened in the longitudinal direction of the knee airbag with respect to the other side wall that faces the knee-tibia region of the passenger, which also constitutes the impact surface. The desired curved or bent cross section is obtained in this way once the knee airbag has been completely filled. Relatively precise sewing processes, which are difficult to automate, must be carried out in order to create the seams required for the shortening effect even if the design of this knee airbag is quite simple.
The class-defining DE 10 2006 051 218 A1 shows a knee airbag with a traction element in the shape of a strap sewn on the side wall thereof, which constitutes the support surface. The second end of this strap is connected to a part that is fixed on the vehicle, so that a force transmission between this part that is fixed on the vehicle and the corresponding side wall pulls the knee airbag into the desired shape. The disadvantage of this is that the assembly in the motor vehicle is relatively complicated, since it is necessary to connect the knee airbag to another vehicle part. A component that is fixed on the vehicle and can correspondingly absorb large forces must also be provided.